Although our overall objectives remain the same, the immediate emphasis of our investigations will be to clarify the characteristics of sprouting and regenerating nerves in the adult CTM. First we will further improve our electrophysiological techniques for mapping the peripheral fields of the major nerves, and subsequently identify accurately by both histochemical (glycogen-depletion) and electrophysiological methods, the exact size and location of the individual motor units, and the distribution of muscle fibres within these. To demonstrate normal and sprouted neuromuscular connections we will establish an appropriate histological technique (cf. Pestronk and Drachman, 1978). Following either nerve sections, or treatment of selected CTM motor nerves employing mino-osmotic pumps containing TTX, colchicine or saline, we will look for possible spatial and temporal constraints on any subsequent collateral sprouting in the CTM of neonatal and mature rats. Additionally the effects of such sprouting on the expression of reflex local sign will also be studied. Finally, we will examine the possibility of selective reinnervation in a partially and totally denervated CTM in the adult rat, especially after the nerves to CTM are cut and deliberately "scrambled" at a region proximal to nerve entry into the muscle.